Hqperactivity is a common consequence of brain damage in man as well as in experimental animals. Restlessness and increased general activity may represent expression of minimal brain damage after various types of toxic exposure. The research described here is an attempt to evaluate the kinds of hyperactivity produced by different kinds of brain damage in rats and to see if anatomical sites of damage can be predicted from the types of behavioral alteration. Two behavioral techniques are being used. One is a general study of activity of rats throughout the 24-hour diurnal cycle in a residential maze equipped with photocells for recording passage of the rats through the runways of the maze. In this maze rats with bilateral lesions of the globus pallidus are chronically hyperactive at night. Rats which have recovered from coma produced by exposure to carbon monoxide are also chronically hyperactive. The second behavioral technique involves time-lapse photography of the same rats in a "free field." From the films the structure of the sequences of behavior acts are analyzed using computer programs. Differences in the structure of hyperactive behavior are being related to different types of brain damage.